Conventional refrigeration does an incredible job keeping food fresh. But that technology hasn't helped desert dwellers without steady electricity. A more recent development in refrigeration—the Zeer pot-in-pot refrigerator—only requires water, sand, and a hot, dry climate to preserve produce through evaporative cooling. Here's how to make the simple gadget.

Materials and Tools Required

two terra cotta pots with a 2-3 inch difference in diameter. The smaller pot should be glazed and preferably lacking a drainage hole. If the inner container is double glazed (on its inner and outer walls), non-potable water—say seawater—can be employed.

a bag of sterile sand

a square of burlap cloth large enough to cover the top of the inner pot

a trowel

Building It

1. If your pots have drainage holes, plug them with a bit of cork, caulk, or other waterproof material. If you don't, moisture from the sand will seep into the lower pot and immerse the stored goods or seep out the bottom of the larger one.

2. Put down a one-inch deep, level layer of sand in the bottom of the large pot. Set the smaller pot on top of that layer and center it in the larger one. Make sure that the smaller pot's lip is even with the larger one's.

3. Fill sand in around the sides of the of the two pots, leaving about an inch of space below the lip.

4. Pour cold water over the sand until it is thoroughly saturated. Put your food into the smaller pot. Cover that with a burlap cloth, also soaked with water. That's it! Just be sure to refill the water regularly, about once or twice a day.

How It Works

The Zeer was developed in 1995 by Mohammed Bah Abba, a Nigerian school teacher that hailed from a family of pot makers. The design is incredibly simple: a glazed earthen ware pot nestled inside a larger, porous one with a layer of wet sand separating them. As the water evaporates through the surface of the outer pot, it draws heat from the inner one, keeping up to 12kg food fresh for as long as three to four weeks without using a single watt of electricity.

For his efforts, Bah Abba was awarded the $75,000 Rolex Award for Enterprise in 2000 and the World Shell Award for Sustainable Development in 2001 to help spur its development. Presently, Bah Abba sells about 30,000 Zeer per year for 200 Nigerian naira ($1.30) a piece.

Why It Matters

For unprotected food in the North African heat, there is no such thing as a shelf life. Fresh fruit and vegetables last maybe a day or two, and meat spoils within hours. This means that most food must be either sold or consumed immediately. Taking produce to market, in Sudan at least, is a task that typically falls on the women. This tight freshness deadline leaves little free time for their education. But if they had to go to market only weekly, rather than daily, they might actually have time for school—that's the promise of the Zeer.

The Zeer benefits not just individuals but the greater Sudanese society as well. Farmers are granted greater negotiating power when they don't have to sell their wares right there and then. Parents see fewer cases of food-borne illness. And when disease does occur, water and temperature-sensitive medicines can also be preserved in the cool pots.

For the rest of the world, the Zeer represents a zero-electricity option for refrigeration. In extended power outages like the ones we've seen this summer, long after the local store sells its last bag of ice, the Zeer could be your best chance to keep critical perishable goods from spoiling in the heat.